service: fix identification of service running on other lcore

The logic to identify if the MT unsafe service is running on another
core can return -EBUSY spuriously. In such cases, running the service
becomes costlier than using atomic operations. Assume that the
application passes the right parameters and reduce the number of
instructions for all cases.

Cc: stable@dpdk.org
Fixes: 8d39d3e237c2 ("service: fix race in service on app lcore function")

Signed-off-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Reviewed-by: Phil Yang <phil.yang@arm.com>
Acked-by: Harry van Haaren <harry.van.haaren@intel.com>

diff --git a/lib/librte_eal/common/rte_service.c b/lib/librte_eal/common/rte_service.c
index b8c465e..c283408 100644 (file)
--- a/lib/librte_eal/common/rte_service.c
+++ b/lib/librte_eal/common/rte_service.c
@@ -360,7 +360,7 @@ rte_service_runner_do_callback(struct rte_service_spec_impl *s,
 /* Expects the service 's' is valid. */
 static int32_t
 service_run(uint32_t i, struct core_state *cs, uint64_t service_mask,
-           struct rte_service_spec_impl *s)
+           struct rte_service_spec_impl *s, uint32_t serialize_mt_unsafe)
 {
        if (!s)
                return -EINVAL;
@@ -374,7 +374,7 @@ service_run(uint32_t i, struct core_state *cs, uint64_t service_mask,
 
        cs->service_active_on_lcore[i] = 1;
 
-       if (service_mt_safe(s) == 0) {
+       if ((service_mt_safe(s) == 0) && (serialize_mt_unsafe == 1)) {
                if (!rte_atomic32_cmpset((uint32_t *)&s->execute_lock, 0, 1))
                        return -EBUSY;
 
@@ -412,24 +412,14 @@ rte_service_run_iter_on_app_lcore(uint32_t id, uint32_t serialize_mt_unsafe)
 
        SERVICE_VALID_GET_OR_ERR_RET(id, s, -EINVAL);
 
-       /* Atomically add this core to the mapped cores first, then examine if
-        * we can run the service. This avoids a race condition between
-        * checking the value, and atomically adding to the mapped count.
+       /* Increment num_mapped_cores to reflect that this core is
+        * now mapped capable of running the service.
         */
-       if (serialize_mt_unsafe)
-               rte_atomic32_inc(&s->num_mapped_cores);
+       rte_atomic32_inc(&s->num_mapped_cores);
 
-       if (service_mt_safe(s) == 0 &&
-                       rte_atomic32_read(&s->num_mapped_cores) > 1) {
-               if (serialize_mt_unsafe)
-                       rte_atomic32_dec(&s->num_mapped_cores);
-               return -EBUSY;
-       }
-
-       int ret = service_run(id, cs, UINT64_MAX, s);
+       int ret = service_run(id, cs, UINT64_MAX, s, serialize_mt_unsafe);
 
-       if (serialize_mt_unsafe)
-               rte_atomic32_dec(&s->num_mapped_cores);
+       rte_atomic32_dec(&s->num_mapped_cores);
 
        return ret;
 }
@@ -449,7 +439,7 @@ rte_service_runner_func(void *arg)
                        if (!service_valid(i))
                                continue;
                        /* return value ignored as no change to code flow */
-                       service_run(i, cs, service_mask, service_get(i));
+                       service_run(i, cs, service_mask, service_get(i), 1);
                }
 
                cs->loops++;